The present invention relates to molding compositions of improved high toughness and hot-water resistance (stability), comprising copolyesters based on polybutylene terephthalate.
Polybutylene terephthalate, in nonreinforced or reinforced form, is a valuable building material with a number of excellent properties, including high rigidity, surface hardness, abrasion resistance, high deflection temperature under load, dimensional stability, and rapid processability into complicated and large molded components by the injection-molding or extrusion techniques.
A marked drawback of such molded components of polybutylene terephthalate is the relatively low notch impact strength whereby the range of application of these molding compositions is considerably restricted. Threfore, there continues to be a need for modifying polybutylene terephthalate in such a way that the resultant material has a higher toughness.
Heretofore, numerous suggestions have been made for producing molding compositions having high notch impact strength by incorporating aliphatic dicarboxylic acids by condensation into polybutylene terephthalate.
Thus, DOS No. 2,651,650 describes copolyesters of terephthalic acid, 1,4-butanediol, and a branched, saturated aliphatic dicarboxylic acid of 7-30 carbon atoms. DOS No. 2,829,624 discloses copolyesters of terephthalic acid, 1,4-butanediol, and a mixture of adipic, glutaric, and succinic acids as injection-molding or extrusion compositions of high toughness. DOS No. 2,707,852 relates to improving the toughness of polybutylene terephthalate by blending it with copolyesters of terephthalic acid, 1,4-butanediol, and an aliphatic dicarboxylic acid of up to 34 carbon atoms. Reinforced molding compositions based on copolyesters of polybutylene terephthalate, formed by incorporating, by condensation, linear aliphatic dicarboxylic acids of 4-40 carbon atoms, are described in DOS No. 2,924,895.
All of these polybutylene terephthalate molding compositions modified by the use of aliphatic dicarboxylic acids as co-components exhibit the substantial disadvantage that, although they show improved notch impact strength compared with the homopolyester, they exhibit drastically reduced rigidity and marked reduction in hot-water resistance.